1. Field of the Invention
This invention relates to a printing machine having upper and lower boxes for receiving upper and lower printing devices respectively, more particularly to a printing machine having an upper box which is supported above a lower box thereof and which can be moved easily and locked securely relative to the lower box.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional printing machine is shown to comprise a machine base 1, upper and lower boxes 2, 3 mounted on the machine base 1, right and left boxes 4, 5 mounted on the machine base 1, and a conveyor 9 passing horizontally between the upper and lower boxes 2, 3 and between the right and left boxes 4, 5. The upper and lower boxes 2, 3 have upper and lower printing devices S mounted therein, respectively. The right and left boxes 4, 5 have right and left printing devices 7 mounted therein, respectively. An ink-supplying device 8 is connected to the upper and lower printing devices 6 and the right and left printing devices 7 through connecting pipes 801. With the above structure, three side faces of a U-shaped workpiece 701 carried by the conveyor 9 can be printed respectively by means of the upper and lower printing devices 6 and the right and left printing devices 7 when the U-shaped workpiece 701 passes between the upper and lower boxes 2, 3 and between the right and left boxes 4, 5. The distance between the upper and lower boxes 2, 3, i.e., the distance between either one of the upper and lower printing devices 6 and the conveyor 9 is adjustable by rotating an operating handle wheel 207. The distance between the right and left boxes 4, 5 is adjustable by rotating an operating handle wheel 402.
Referring to FIG. 3, an adjustable support device is employed to support the upper box 2 on the lower box 3 in a vertically movable and adjustable position. The adjustable support device includes two dovetailed tenons 204 formed on two opposite sides of the upper box 2, and two dovetailed grooves 304 formed on two opposite sides of the lower box 3. The tenons 204 are received respectively in the grooves 304 so that the upper box 2 is disposed slidably on the lower box 3. A support block 205 is fixed to the upper box 2. A locking block 305 is fixed to the lower box 3. A threaded shaft 208 extends through a threaded hole 206 in the support block 205 and the locking block 305. The threaded shaft 208 has a diameter-reduced lower end portion 209 engaging a locking pin 306 in the locking block 305 such that the threaded shaft 208 is rotatable but not movable in the axial direction with respect to the locking block 305. When the handle wheel 207, and therefore the threaded shaft 208, is rotated, the upper box 2 can move vertically with respect to the lower box 3, thereby resulting in a desired gap between the upper and lower boxes 2, 3 to permit a workpiece of specified size to pass therebetween.
The adjustable support device suffers from the following disadvantages:
1. Since the adjustable support device has no positioning means to position the upper box 2 relative to the lower box 3 after the upper box 2 is moved to a desired position, the upper box 2 may move downward gradually by virtue of its weight. Thus, the distance between the upper and lower boxes 2, 3 is reduced undesirably. Therefore, the workpiece 701 may be prevented from passing through the upper and lower boxes 2, 3. PA1 2. Since the rotary shaft extends vertically through the upper box 2, and since the handle wheel 207 is located on the top of the upper box 2 at a relatively high position, the operation of the handle wheel 207 is relatively inconvenient to conduct.